The overall objective of this research is to elucidate the comparative biochemistry and physiological role of carbohydrate-specific clearance processes which mediate the removal of glycoproteins from the circulation. Our immediate objectives are: a) to use RNase B as a probe to complete the characterization of the system responsible for the rapid clearance of alpha-mannosyl-terminal glycoproteins from plasma, with particular attention to the organ-site(s) and cellular receptors involved in the uptake process; b) to investigate the role of alpha-mannosyl-terminal oligosaccharide side chains of lysosomal glycosidases in mediating the rapid hepatic clearance of these enzymes, using beta-glucuronidase as a model lysosomal enzyme, and c) to initiate studies with glycosidase digested RNase C to determine the effects of exposed galactosyl and N-acetylglucosaminyl residues on the kinetcs and sites of clearance of these modified RNase C's from the circulation. 125I-RNase B will be used to identify sites of clearance of RNase B from the circulation, and to determine the metabolic fate of the RNase B following uptake. Preliminary experiments have shown that the liver is a primary site of RNase B clearance. Therefore using insolubilized RNase B as an affinity column, efforts will be directed toward the isolation and characterization of an alpha-mannoside binding protein from liver membranes. Parallel studies with beta-glucuronidase, using glycosidase treatment and competition experiments with RNase B, will attempt to determine whether the mechanism for clearance of RNase B also operates on the lysosomal glycosidases. The studies with asialo- and agalacto-RNase C will complement those with RNase B, and are designed to permit a direct comparison of the biochemistry and physiology of carbohydrate-specific clearance processes operating on an identical polypeptide chain bearing various terminal carbohydrate residues.